1. Technical Field
The present invention relates to harmonic drives, and more particularly to a harmonic drive featuring helix-facilitated lubrication.
2. Description of Related Art
A harmonic drive is a reducer featuring high reduction ratio. It conventionally comprises a circular spline, a flexspline positioned inside the circular spline, and a wave generator rotatably installed in the flexspline. When the wave generator is assembled in the flexspline, the flexspline deforms into an elliptic shape as it is pressed by the outer periphery of the wave generator from inside. Thereby, when the wave generator is driven by a power source to rotate, the circular spline and the flexspline mesh with each other fittingly at the major axis of the wave generator, and leave each other completely at the minor of the wave generator. Since the circular spline and the flexspline have different numbers of teeth, when the wave generator continuously rotates, the difference of the numbers of teeth provides reduction, thereby generating high-torque output.
For reducing wear against such a harmonic drive and maximizing its service life, many designs for lubrication have been implemented in the prior art. For example U.S. Pat. No. 7,905,326 involves filling lubricant into a lubricant-feeding hole on the flexspline through a lubricant-feeding channel formed in the circular spline, so as to lubricate the wave generator. However, since the flexspline continuous deforms during operation, stress tends to concentrate on the site of the lubricant-feeding hole and structurally damage the flexspline. Another known approach, as disclosed in Japan Patent No. JPY1994015151, involves assembling the flexspline and a lubricant-holding mechanism together by means of a mortise-tenon structure. However, this design may cause additional impacts among the lubricant-holding mechanism, the bearing and the flexspline, and adversely affect the overall lubrication efficiency.